The wipe tower's "Delay after unloading" never happened on Klipper. It was
emitted as G4 S<seconds>, and Klipper's G4 reads only the P parameter, in
milliseconds, so the pause was silently skipped. The option now produces a
dwell Klipper actually performs.
Also corrects the planner flush rationale, which cited an extruder position
reset that Klipper resolves at parse time and does not need synchronized, and
adds end-to-end coverage that slices a two-filament print and checks the
emitted wipe tower G-code on both a Klipper and a non-Klipper flavor.
No change to any other firmware flavor's output, and no shipped profile sets a
non-zero delay, so no shipped profile's output moves either.
The wipe tower emitted G4 S0 to make the firmware finish its queued moves
before commands that must not take effect early. Klipper's G4 reads only the
P parameter, so that flush never happened there and a temperature change could
land seconds ahead of the moves it was meant to follow. Klipper now gets M400
instead, through one helper shared by both wipe tower implementations.
No change to any other firmware flavor's output, so no shipped profile or saved
project is affected.
